Savings goal calculator
How much to put aside each month, or how long a goal takes at a given contribution.
Fill in the fields and the result will appear here automatically.
A savings target can be solved for a deadline or a fixed monthly contribution. The model separates initial savings, later deposits and interest. Interest applies to the previous balance before a month-end contribution is added, so that deposit earns interest from the following month. A constant nominal rate is a scenario assumption, rather than a guaranteed return or a convention shared by every savings product.
How it works
Formula and logic
With i = r/1200, month-n balance B = I(1+i)^n + C[(1+i)^n−1]/i. At i = 0, B = I+nC. A specified duration solves for C, with a floor of zero. For a contribution, the first whole month reaching G is found: at i > 0 the real-valued term is log[(G+C/i)/(I+C/i)]/log(1+i), followed by checks of adjacent months. If I ≥ G, duration is zero. There is no arbitrary century cutoff; unrepresentable values produce a range message.
Example
Target 1,000,000, initial 100,000, rate 8% and five years give monthly contribution 11,582.09; unrounded contributions over 60 months total 694,925.29. Target 121, initial 100, rate 12% and deposit 10 give balances 111 after one month and 122.11 after two, reaching the target in two months. Target 10,000 with initial zero, rate 0% and deposit 1 needs 10,000 months.
Fields and units
- What to work out — list option
- Goal amount — $
- Already saved — $
- Annual rate, % — unitless
- Term, years — years
- Monthly contribution — $
How to use
- — Choose contribution from duration or duration from contribution.
- — Enter a positive target, starting savings and nominal rate from 0 to 100%; blank starting savings means zero.
- — For the contribution, supply years rounded to the nearest whole month. For duration, supply a positive monthly deposit.
- — Use one currency, then assess fees, taxes and purchasing-power changes separately.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- Microsoft FV: initial amount, regular deposits and deposit timing Microsoft NPER: period count with constant rate and payments
- Limitation
- Constant nominal return and month-end contributions. Taxes, fees, inflation and rate changes are excluded; this is not a forecast for a specific savings product.
FAQ
When does a monthly savings deposit start earning interest?
It is added after interest at month-end and earns from the next month. Beginning-of-month deposits would give a different balance.
Can the savings duration be solved without a monthly loop?
Yes. Constant rates and deposits allow a logarithmic formula, then the first whole month is checked. A changing rate needs a different scenario.
Why can the first target-month balance exceed the goal?
The result is a full month with a full deposit, rather than a fractional month or reduced final contribution. The target can therefore be exceeded.
How does the savings target work at zero interest?
The balance is linear: I+nC. A goal of 10,000 and deposit 1 from zero take 10,000 months, a finite duration even though it exceeds a century.
Does the rounded savings contribution hit the goal exactly?
The formula uses unrounded contributions while the screen shows two decimals. Depositing the rounded amount may require a small last-deposit adjustment. Taxes, fees and inflation are not deducted.